Mechanical blood pumps are commonly applied to temporarily support the pumping function of the heart during heart surgery or during periods of heart failure. The most widely applied devices include roller pumps and centrifugal pumps currently used in more than 400,000 cases of heart surgery annually. Usually, the pumps comprise part of a cardiopulmonary bypass circuit in which many components are combined including an oxygenator, a heat exchanger, blood reservoirs and filters, and many feet of tubing to transport the blood from the patient on the operating table to the heart-lung machine located nearby and back to the patient. Blood is withdrawn from the patient via uptake cannulae placed into the vena cavae and atria or ventricles of the heart and pumped back into the pulmonary artery and aorta via return cannulae. The system generally works well but is complicated and expensive, exposes the blood to a high surface area of foreign materials which causes damage, requires full anticoagulation, and requires considerable time to set up and manage by a skilled technician.
In most cases of coronary artery bypass surgery the heart is cooled and stopped and an oxygenator is used although it is not necessary to actually open the heart as it is with valve surgery. In a few cases, the oxygenator is omitted from the system and the patients own lungs continue to function during the course of the surgical procedure. In such cases, either the pumping function of the left ventricle alone or both the left and right ventricles, is supported mechanically. Pulsatile pumps and continuous flow pumps have been used experimentally and in human cases. The heart is not cooled and is not stopped, although drugs may be given to slow its rate. The procedure has a number of important advantages in appropriate cases, however, present blood pumps, cannulae, and tubing sets have not been developed specifically for this application, and setup, cannulation, priming, and patient management during the procedure are somewhat makeshift and leave room for considerable improvement. The cannula pump of the present invention is especially suited to this use, and greatly simplifies the procedure, reducing the number of cannulation sites, reducing the surface area of foreign materials, reducing the priming volume and setup time, and permitting very simple management of heart function during the procedure.
To support the systemic circulation, a single cannula containing a miniature rotary pump is inserted into the heart, via a small incision, and both the necessary inflow and outflow connections are accomplished immediately. The blood pump may be inserted via the apex of the ventricle, the atrium, or the aorta, but in each case only one cannulation is necessary. The pump itself resides within the cannula and is connected by a short drive shaft to a small motor outside the heart, usually positioned immediately adjacent to the heart in direct connection with the cannula. If support of the pulmonic circulation is required, this is also achieved by a single cannulation via the right ventricle, right atrium, superior vena cava, or pulmonary artery. Thus, to support the total function of the heart, two cannula pumps, each requiring only one cannulation site, are used.
Cannula pumps are advantageous in cases requiring emergency circulatory support where the chest can be rapidly opened for access to the heart and the simple cannula pump can be inserted immediately. Because no cumbersome or large equipment is involved, the device can be applied in tight quarters, where use of larger more complicated systems is precluded, and in cases of cardiac arrest where there is inadequate time to setup and prime other devices. Examples include ambulance, aircraft, emergency room, cardiac cath lab, and rescue or military use in the field.